1. Field of the Invention
The present invention relates to elements of magnetic circuits having a star configuration and, more specifically, to their application to polyphase transformers.
2. Description of the Prior Art
Conventionally, the polyphase transformers, and more specifically the three-phase transformers, are of the E-type, that is with three core-columns in a same plan, or of the five columns type or of the shell-type.
Referring to conventional theoretical books on the polyphase transformers, (in particular the "Cours de Machines Electriques", C.N.A.M. Editions de M. Bellier or "Electrotechnique generale", Editions Scientifiques Riber, tome 3 of A. Busson), it will be appreciated that those three types of transformers have the drawback of a non-symmetrical magnetic circuit as the length of the frame to be crossed by the magnetic flux is not the same from a side column to the central column or to the other side column. Various means are used for palliating this dissymmetry; however, the magnetic circuit of those devices remains non-symmetrical and it is easy to measure that the no-load currents are not identical in the three phases and the power absorbed by each phase is different from the others. In the general purpose conventional books about polyphase transformers, it will be appreciated that there is generally an introductory paragraph wherein it is explained that a transformer having a star configuration would be ideal for obtaining a three-phase symmetrical transformer but that such a configuration cannot be practically achieved as it would cause the presence of gaps in the central part of the magnetic circuit forming the star, such gaps would be difficult to tighten and would cause important losses in the magnetic circuit.